<I>In vitro</I> and <I>in vivo</I> antibacterial activity of sitafloxacin

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  • Sitafloxacinの細菌学的評価

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Abstract

The in oitro and in vivo antibacterial activity of sitafloxacin (STFX), a quinolone, was compared to that of other quinolones: levofloxacin, ciprofloxacin (CPFX), moxifloxacin, and tosufloxacin. STFX showed the most potent antibacterial activity against clinical isolates of both Gram-positive and Gram-negative bacteria, including quinolone-resistant strains, Mycoplasma pneumoniae, and Chlamydiaceae. MIC90 of STFX against streptococcus pneumoniae, a major respiratory tract infection pathogen was 0.06μg/mL, and was 4-to 64-fold more active than those of other quinolones tested. MIC90 of STFX against Escherichia coli, major urinary tract infection pathogen, was 1μg/mL, and was 16-to 32-fold more active than those of other quinolones tested. In systemic infection caused by major pathogens in mice, STFX showed a protective effect reflecting its potent in vitro antibacterial activity. STFX also showed higher in vitro activity against Pseudomonas aeruginosa than that of CPFX. In a model of complicated urinary tract infection caused by P. aeruginosa in the rat, the therapeutic efficacy of STFX was greater than that of CPFX. A study on the inhibitory effect against DNA gyrase and topoisomerase IV purified from S.pneumoniae and E. coli showed that STFX had higher inhibitory activity than other quinolones tested against both wild-and mutant enzymes, which has single or double aminoacid replacement (s) in the quinolone-resistance-determining region (QRDR). The inhibitory activity of STFX against mutant DNA gyrase and topoisomerase IV, which has single amino-acid replacement in QRDR, corresponded roughly to those of other comparable quinolones against wild-type enzymes.<BR>In an in vitro pharmacokinetic model simulating serum concentrations of STFX following 50mg twicedaily and 100mg twice-daily oral administration, STFX was shown to be bactericidal against staphylococcas aureus, S.pneumoniae, E.coli, P. aeruginosa, Haernophilus influenzae, and Moraxella catarrhalis. Even at lower doses, STFX was bactericidal against S. pneumoniae, H. influennzae, and M. catarrhalis, for which MIC of STFX corresponded to MIC90 of clinical isolates. A study focusing on AUC, the malor pharmacokinetic parameter correlated with pharmacodynamics of quinolones, showed that STFX, with simulated human serum AUC in the mouse, was shown to be highly effective in a model of pneumonia due to penicillin-resistant S.pneumoniae.

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